Apparatus for regulation of airflow to flame tubes for gas turbine engines

ABSTRACT

An annular flame tube for a gas turbine engine includes a primary combustion air inlet, a plurality of secondary combustion air inlets and variable air flow restricting means associated with at least some of the inlets, the restricting means being expandable in response to temperature or pressure to vary the ratio of primary combustion air to secondary combustion air.

United States Patent Jackson et al.

[ 1 Sept. 19, 1972 APPARATUS FOR REGULATION OF AIRFLOW TO FLAME TUBES FOR GAS TURBINE ENGINES Inventors: Squire Ronald Jackson, 250

Manchester Road; Kenneth Greenwood, 585 Brumshaw Road, both of Bumley; Alban Heaton, l6 Dawnham Ave., Gt. Harwood near Blackburn; Alwin Harrison, 7 Standen Hall Drive Lanehead, Burnley, all of England Filed:- Oct. 29, 1970 Appl. No.: 85,181

' Related U.S. Application Data Division of Ser. No. 783,009, Dec. 11, 1968, Pat. No. 3,577,878.

Foreign Application Priority Data Nov. 10, 1967 Great Britain 31293157 U.S. Cl so/39.23, 60139.29 Int. Cl ..F02c 9/14 Field of Search ..60/39.23, 39.29, 39.65

Primary Examiner-Carlton R. Croyle Assistant Examiner-Robert E. Garrett Attorney-Holman & Stern [57] ABSTRACT An annular flame tube for a gas turbine engine includes-a primary combustion air inlet, a plurality of secondary combustion air inlets and variable air flow restricting means associated with at least some of the inlets, the restricting means being expandable in response to temperature or'pressure to vary the ratio of primary combustion air to secondary combustion air.

6 Claims, 6 Drawing Figures PATENTEDSEH I 3.891.761

- SHEET 2 OF 4 FIG. 2.

8 0 FIG. 5.

' INVENTOE M wim ddw%mf%q g ATTORNEYS PATENTED 1 i 31691; 76 1 SHEET 3 BF 4 I INVENTOE APPARATUS FOR REGULATION OF AIRFLOW TO FLAME TUBES FOR GAS TURBINE ENGINES This invention relates to flame tubes for gas turbine engines and is a divisional application from our Ser. No. 783,009, now U.S. Pat. No. 3,577,878, filed Dec. ll, 1968.

In the flame tubes of such engines, it is the practice for a minor amount of air, about -40 percent of the total air intake, to be employed for the combustion of fuel, the remainder being employed for cooling the flame tube, diluting of the flame and of the products of combustion before the latter are allowed to enter the turbine stage of the engine. The air for combustion purposes is itself normally separated into primary and secondary streams entering along separate paths to the interior of the flame tube. In some engines which are required to operate over a wide range of fuel/air ratios, the combustion and dilution air quantities over some parts of the operating range are incorrect thus impairing combustion efficiency and giving rise to. loss of performance over that part of the engine operating range.

The object of the invention is to provide a flame tube for a gas turbine engine in which this disadvantage is overcome or reduced.

In accordance with the invention there is provided an annular flame tube for a gas turbine engine having an annular chamber having an annular primary combustion air inlet passage and at least one co-axial annular secondary combustion air inlet passage opening into the said chamber downstream of the said primary combustion air inlet passage and variable air flow restricting means associated with at least some of the said inlets, the said air flow restricting means being expandable in response to an increase in a control quantity to vary the ratio of primary combustion air to secondary combustion air.

Reference is now made to the accompanying drawings in which:

FIG. 1 is a partial section through an annular flame tube incorporating one example of the present invention,

FIG. 2 is a view on arrow 2 in FIG. 1, and

FIGS. 3 to 6 show alternative embodiments of the invention.

The flame tube shown in FIGS. 1 and 2 has an annular combustion chamber enclosed by an external tube member 31 and an internal tube member 32. Burners 33 are located in the upstream end 30a of the chamber 30. Primary combustion air also enters the chamber 30 at the end 30a thereof. Within the space defined between the chamber 30 and member 31 are a series of louvre-type flow restrictors 90 controlling ducts 91 terminating in nozzles 92 whereby secondary air enters primary air flow and the flame. The louvres 90 are movable by means of a Bourdon tube 93 which receives pressure from a common manifold 94. Dilution air enters the combustion chamber 30 at a position downstream of the secondary air inlet nozzles 92 via nozzles 95 which are controllable by closure members 96 movable into the nozzles 95 by means of pressure operable bellows 97.

FIG. 3 shows an annular primary air conduit wall 140 having positioned circumferentially thereabout a plurality of bimetallic segments 141a. The flame tube has a series of the conduits 140 opening via swirlers 143 in a common annular combustion space. A burner (not shown) extends into the combustion space through the swirler 143. The bimetallic strips 141a each have an angled end piece 141b, these end pieces being directed slightly in the direction of air flow through the conduit. On heating the bimetallic strips by means of the electrically heated retaining ring 142, the angled pieces l4lb are caused to project across the cross section of the conduit in order to restrict air flow to the desired extent.

Secondary combustion air and dilution air is supplied to the combustion space through a pair of annular passages in a like manner to that shown in FIG. 1. In use, the outer ends of the segments 141a are heated to effect deflection thereof towards the axis of the conduit, thereby restricting airflow through the conduit and consequently varying the ratio of primary to secondary and dilution air.

The embodiment shown in FIG. 4 has a flow restrictor comprising four curved shutters 150, I51 and 152, 153 each of which is movable radially into the primary flow conduit through slots in an annular wall 154. The segments 150, 151 are provided with integral lugs 155, 156 respectively and each of which has a pin 157 which extends through a slot in an eye 158 secured to one end of a pair of bimetallic strips 159, 160 interconnected to a common electrically heated element 161. The shutters I52, 153 are also connected in a similar fashion to double bimetallic strips 162, 163 which are in turn connected to heating element 164. In operation, the heating elements control radially inward or outward movement of the shutters to restrict the flow path for prim ary air. It should be noted that FIG. 4 shows the shutters 150, 151 closed and the shutters 152, 153 open. This condition does not, of course, occur in actual use.

The embodiment shown in FIG. 5 comprises arcuate Bourdon tubes connected at one end to a pressure manifoled 181. The other end of each' tube 180 has a pin 182 which is slidable within a slot 183 in any eye 184 at one end of restrictor segments 185 which extend into the conduit, the restrictor segments being pivoted at 186. On pressure being applied within the tubes 180, the tubes 180 tend to extend so as to pivot the element 185 about pivots 186 to remove the elements 185 from the conduit thereby derestricting air flow therethrough. On removal of pressure from the tubes 180 the elements 185 are pivoted to extend into the conduit to restrict air flow therethrough. There are a series of the segments 186 about the conduit, each having its own Bourdon tube.

The arrangement shown in FIG. 6 embodies a solid spiral restrictor 200. Extension and retraction of the restrictor 200 is effected by a pressurizable bellows 201 slidably mounted on a central spindle 202 through the intermediary of sealing rings 203. The interior of the bellows is in communication with the exterior of the conduit through the intermediary of a pipe 204. In this embodiment, increase in pressure within the bellows 201 causes extension of the bellows which results in closure of the spiral restrictor 200 and hence restriction of the primary air conduit.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. An annular section flame tube for a gas turbine engine comprising an annular chamber having a primary combustion air inlet passage and at least one annular secondary combustion air inlet passage coaxial with the chamber and opening into the said chamber downstream of the said primary combustion air inlet passage and variable airflow restricting means associated with at least some of the said inlets, the said airflow restricting means being expandable in response to an increase in an independently variable control signal to vary the ratio of primary combustion airto secondary combustion air. I

2. A flame tube as claimed in claim 1 in which the flow restriction means is associated with the primary combustion air inlets and includes bimetallic elements and heating elements for said bimetallic elements.

3. A flame tube as claimed in claim 2 in which the bimetallic elements are arranged outside the inlets and flow restricting means comprise a closure member as sociated with each inlet and movable with respect to the associated inlet by means of a bellows.

6, A flame tubeas claimed in claim 5 in which the closure member comprises a spiral restrictor deformable bythe bellows.

w a: n: r s 

1. An annular section flame tube for a gas turbine engine comprising an annular chamber having a primary combustion air inlet passage anD at least one annular secondary combustion air inlet passage coaxial with the chamber and opening into the said chamber downstream of the said primary combustion air inlet passage and variable airflow restricting means associated with at least some of the said inlets, the said airflow restricting means being expandable in response to an increase in an independently variable control signal to vary the ratio of primary combustion air to secondary combustion air.
 2. A flame tube as claimed in claim 1 in which the flow restriction means is associated with the primary combustion air inlets and includes bimetallic elements and heating elements for said bimetallic elements.
 3. A flame tube as claimed in claim 2 in which the bimetallic elements are arranged outside the inlets and are coupled to restrictor elements extending into the inlets.
 4. A flame tube as claimed in claim 1 in which the flow restriction means comprises Bourdon tubes movable between restricting and non-restricting positions by the application of fluid pressure thereto.
 5. A flame tube as claimed in claim 1 in which the flow restricting means comprise a closure member associated with each inlet and movable with respect to the associated inlet by means of a bellows.
 6. A flame tube as claimed in claim 5 in which the closure member comprises a spiral restrictor deformable by the bellows. 